As known, many pourable food products, such as fruit juice, UHT (ultra-high-temperature treated) milk, wine, tomato sauce, etc., are sold in packages made of sterilized packaging material.
A typical example of this type of package is the parallelepiped-shaped package for liquid or pourable food products known as Tetra Brik Aseptic (registered trademark), which is made by folding and sealing laminated strip packaging material.
The packaging material has a multilayer structure substantially comprising a base layer for stiffness and strength, which may comprise a layer of fibrous material, e.g. paper, or mineral-filled polypropylene material, and a number of lamination layers of heat-seal plastic material, e.g. polyethylene films, covering both sides of the base layer.
In the case of aseptic packages for long-storage products, such as UHT milk, the packaging material also comprises a layer of gas-barrier material, e.g. aluminium foil or ethyl vinyl alcohol (EVOH) film, which is superimposed on a layer of heat-seal plastic material, and is in turn covered with another layer of heat-seal plastic material forming the inner face of the package eventually contacting the food product.
Packages of this sort are normally produced on fully automatic packaging machines, on which a continuous tube is formed from the web-fed packaging material; the web of packaging material is sterilized on the packaging machine, e.g. by applying a chemical sterilizing agent, such as a hydrogen peroxide solution, which, once sterilization is completed, is removed from the surfaces of the packaging material, e.g. evaporated by heating; the web of packaging material so sterilized is then maintained in a closed, sterile environment, and is folded and sealed longitudinally to form a vertical tube.
The tube is filled with the sterilized or sterile-processed food product, and is sealed and subsequently cut along equally spaced cross sections to form pillow packs, which are then folded mechanically to form respective finished, e.g. substantially parallelepiped-shaped, packages.
Alternatively, the packaging material may be cut into blanks, which are formed into packages on forming spindles, and the packages are filled with the food product and sealed. One example of this type of package is the so-called “gable-top” package known by the trade name Tetra Rex (registered trademark).
To open the packages described above, various solutions have been proposed, including reclosable opening devices made of plastic material and substantially comprising a pouring element, e.g. a spout, defining a through opening and fitted to a hole in a wall of the package.
When producing one type of opening device, the opening of the pouring element is sealed by a plastic confetti portion connected integrally to the pouring element and detachable from it along a smaller-section annular tearable membrane.
A removable, e.g. screw or hinged, cap can be fitted to the pouring element to outwardly close the latter and to allow closure of the package after the first opening by removing the confetti portion.
On the side destined to face the cap, the confetti portion may have an integral projecting pull ring, the free end of which is pulled by the user to detach the confetti portion from the pouring element along the tearable membrane and so open the product pour opening.
In the case of packages requiring not only liquid but also gas sealing, the opening devices are fitted to removable portions of the packaging material rather than to holes formed in the packaging material. In one such known solution, the confetti portion of the opening device is fixed directly to a pre-laminated hole in the packaging material, i.e. a hole formed in the base layer only and covered by the other lamination layers, including the layer of gas-barrier material.
The above-described opening devices can be produced and applied directly on the edges of the holes formed in the packaging material or on the above-described pre-laminated holes by injection molding operations.
In such method of applying opening devices, the packaging material is advanced along a given path and is stopped when one of its holes or pre-laminated holes is interposed between, and faces, two molds of a molding unit in an open configuration.
At this point, the molds are displaced towards the packaging material to reach a closed configuration, in which they cooperate with opposite faces of the packaging material and define a closed mold cavity housing the hole or the pre-laminated hole on which the opening device is to be formed. The injection molding operation is then performed by injecting the molten plastic material in the mold cavity defined by the molds in the closed configuration.
In the case of an opening device formed on a hole of the packaging material, the molten plastic material is injected into the mold cavity from one side thereof and is forced to flow within the mold cavity to fill it completely. When the molten plastic material sets, the molds are opened and the packaging material can be again advanced to take a new hole between the open molds for forming another opening device.
In the case of an opening device formed on a pre-laminated hole of the packaging material, the molten plastic material is injected onto one side of the pre-laminated hole to cover it up to an annular peripheral portion thereof and to form, in this way, a plastic confetti portion directly attached to the pre-laminated hole; the molten plastic material is then forced to pierce the pre-laminated hole at such annular peripheral portion to form a pouring element of the opening device projecting from an opposite side of the pre-laminated hole and attached to the confetti portion through a smaller-section annular membrane connection portion adapted to be torn by the user to open the package. In this way, the material forming the pre-laminated hole is first pierced through and then resealed by the plastic material forming the pouring element.
Injection molding apparatus of the type described above are used widely and satisfactorily to form opening devices directly on a sheet packaging material. Within the industry, however, a demand for further improvements is felt, particularly in view of the continual request to increase the output rate of the packaging machines and to decrease the footprints thereof.
It is in fact evident that, due to the indexed motion applied to the packaging material to form the opening device on the holes or pre-laminated holes of the packaging material, an increase of the output rate may be only obtained by adopting a large number of molding units with a consequent increase of the footprint of the molding apparatus.
In addition, by using the above-described molding apparatus with multiple molding units, possible errors in the distances between each hole or pre-laminated hole and the adjacent ones necessarily require position corrections by acting on the packaging material between each molding unit and the following one, with further increase of the footprint of the apparatus, reduction of the output rate and increased risks to produce damages or undesired marks on the packaging material.